Intermetallic Compound Grains Research Articles

Influence of Welding Speed on Characteristics of Non-Axisymmetric Laser-Tungsten Inert Gas Hybrid Welded Mg/Al Lap Joints with Zn Filler.

A non-axisymmetric laser-tungsten inert gas (TIG) heat source was designed to join Mg–Al dissimilar metals with pure Zn filler at a series of welding speeds (500–900 mm/min). Laser and TIG heat sources respectively acted on Al and Mg base metals to precisely control their dissolution into the welding pool. The solidification rate of liquid metal was controlled by adjusting the welding speed, then the reaction process of Mg, Al and Zn could be accurately regulated. The results indicated that various microstructures including Al solid solution, Zn solid solution, Mg–Zn intermetallic compounds (IMCs) and eutectic structure formed in the joint produced at different speeds. Lower welding speed (500 mm/min) caused the microstructure coarsening and higher welding speed (900 mm/min) would lead to the enrichment of MgZn2 intermetallic compounds. At the optimal welding speed of 800 mm/min in particular, fine MgZn2 IMCs grains uniformly distributed in the Al and Zn solid solution. The tensile-shear load reached a maximum of 1052.5 N/cm and the joint fractured at the fusion zone near the Al base metal.

Interfacial transfer and phase evolution between Cu and Sn solder doped with minor Cu, Ag and Ni: experimental and theoretical investigations

The effects of minor Cu (0.7%), Ag (3.5%) and Ni (0.1%) additions in Sn solder on the interfacial transfer and phase evolution were clarified in Sn/Cu solder joints. (Cu,M)6Sn5 and (Cu,M)3Sn (M = Cu, Ni) layers were observed at the Sn/Cu interface during thermal aging at 150 °C. The additions of Cu, Ag and Ni alloy elements were found to change the growth of the Cn–Sn intermetallic compounds (IMCs). The results showed that Cu, Ag and Ni additions were able to suppress the growth of (Cu,M)3Sn (M = Cu, Ni) layers, but promoted the (Cu,M)6Sn5 growth. This was because the reactions on the (Cu,M)6Sn5 side were promoted by the refined IMCs grain size, whose growth was at the expense of (Cu,M)3Sn. In addition, the interfacial transfer rate (thickness ratio, y) of (Cu,M)3Sn/(Cu,M)6Sn5 versus the thermal aging time (t) was found to be close to parabola relationship, the y increased gradually with the alloy elements from Ni, Cu to Ag. The phase evolution (η′-Cu6Sn5, η-Cu6Sn5, e-Cu3Sn, Ag3Sn, η′-(Cu,Ni)6Sn5, η-(Cu,Ni)6Sn5 and e-(Cu,Ni)3Sn) at the interface between Cu and Sn solder doped with minor Cu, Ag and Ni was also elucidated.

Integration of machine learning with phase field method to model the electromigration induced Cu6Sn5 IMC growth at anode side Cu/Sn interface

Currently, in the era of big data and 5G communication technology, electromigration has become a serious reliability issue for the miniaturized solder joints used in microelectronic devices. Since the effective charge number (Z*) is considered as the driving force for electromigration, the lack of accurate experimental values for Z* poses severe challenges for the simulation-aided design of electronic materials. In this work, a data-driven framework is developed to predict the Z* values of Cu and Sn species at the anode based LIQUID, Cu6Sn5 intermetallic compound (IMC) and FCC phases for the binary Cu-Sn system undergoing electromigration at 523.15 K. The growth rate constants (kem) of the anode IMC at several magnitudes of applied low current density (j = 1 × 106 to 10 × 106 A/m2) are extracted from simulations based on a 1D multi-phase field model. A neural network employing Z* and j as input features, whereas utilizing these computed kem data as the expected output is trained. The results of the neural network analysis are optimized with experimental growth rate constants to estimate the effective charge numbers. For a negligible increase in temperature at low j values, effective charge numbers of all phases are found to increase with current density and the increase is much more pronounced for the IMC phase. The predicted values of effective charge numbers Z* are then utilized in a 2D simulation to observe the anode IMC grain growth and electrical resistance changes in the multi-phase system. As the work consists of the aspects of experiments, theory, computation, and machine learning, it can be called the four paradigms approach for the study of electromigration in Pb-free solder. Such a combination of multiple paradigms of materials design can be problem-solving for any future research scenario that is marked by uncertainties regarding the determination of material properties.

Influence of External Interface Normal Stress on the Growth of Cu–Sn IMC During Aging

A U-shape clamp was designed to apply stress perpendicular to the interface of Cu/Sn/Cu solder joints, and its influence on the growth behavior of Cu–Sn intermetallic compound (IMC) during thermal aging at 150 °C was investigated. The results show that compared with the sample at general stress-free state, the growth rate of IMC under compression is faster, while that under tension is slower. Moreover, the interface between IMC and Sn is smoother under compressive stress, and the corresponding IMC grains are smaller and more uniform than that under tensile stress. According to the growth kinetic analysis, the growth of IMC under general, compressive and tensile states is all controlled by the combination of grain boundary diffusion and volume diffusion with a similar growth exponent (n ≈ 0.4). However, external stress can affect the Ostwald ripening process of grain growth, causing a change of grain size and grain boundary density in the IMC layer. As a result, the IMC growth behavior at the interface of the solder joint will be affected by the applied external normal stress.

Electromigration in Bi-crystal pure Sn solder joints: Elucidating the role of grain orientation

Intermetallic compound (IMC) and void growth are electromigration (EM) damage mechanisms that are controlled by the anisotropic diffusion of Cu in β-tetragonal Sn solder joints. Single crystal fast diffusion, slow diffusion, and bicrystal solder joints were fabricated and tested under thermal aging and EM conditions to investigate the effect of grain orientation on microstructure evolution including IMC growth, void growth and grain structure. Sample and testing geometry ensured there were no effects from current crowding or joule heating so that crystallographic effects could be isolated. Microstructure characterization by scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and X-ray microtomography revealed interface-nucleated and bulk-nucleated IMC growth, particle stimulated nucleation (PSN) of recrystallized grains, and two unique voiding behaviors, void faceting and void burrowing. The relationship between these features and β-Sn grain orientation and implications for EM damage mitigation are discussed.

A diffusion model and growth kinetics of interfacial intermetallic compounds in Sn-0.3Ag-0.7Cu and Sn-0.3Ag-0.7Cu-0.5CeO2 solder joints

The growth kinetics of the intermetallic compounds (IMCs) between the low-silver composite solders (Sn–0.3Ag–0.7Cu-xCeO2) and copper substrates during reflow soldering process has been studied in this work. The thickness and grain size of the interfacial IMCs increase with an increase of reflow time. The addition of CeO2 nanoparticles can effectively suppress the growth of the interfacial IMCs. The interfacial reaction between composite solders and copper substrates is a dynamic response to the comprehensive effects of IMC growth at the interface, diffusion rate of copper atoms, and changes in composition at the solder/copper interface. A diffusion-controlled kinetics model is put forward to investigate the comprehensive effects. The modeling results show that, the diffusion rate of copper atoms at the solder/copper interface is related to the interfacial IMC grain size, IMC thickness and reaction time, and the addition of CeO2 nanoparticles can lead to a relatively lower diffusion rate of Cu atoms at the solder/copper interface. The change characteristic of the copper atom diffusion introduced in this model is supported by a good agreement between experimental and theoretical results. The mechanism of CeO2 nano-additive on the diffusion behavior of Cu atoms at the interface and interfacial IMC growth is explained by using the theory of adsorption and heterogeneous nucleation.

Effect of polycrystalline Cu microstructures on IMC growth behavior at Sn/Cu soldering interface

This paper investigated the morphologies of intermetallic compounds (IMCs) forming between pure Sn solders and different polycrystalline copper substrates with microstructures of fiber structure, equiaxed crystal and columnar crystal respectively as well as the effect of Cu microstructures on IMC growth kinetics. The results showed that when multiple IMC grains could be accommodated in a single grain area of substrates, the IMC growth behavior on some grains of polycrystalline substrates was similar to that on single crystalline substrate of same orientation. The difference on polycrystalline Cu substrates was that IMCs with different morphologies appeared alternately. Furthermore, the IMC distribution at soldering interface was stripy on fiber structure and blocky on equiaxed crystal substrates. With increasing of reflow temperature or time, IMCs with different morphologies followed their own growth behavior. In addition, the grain growth rate of IMCs on columnar crystal substrate was higher than that on the other two substrates due to different Cu supply and diffusion abilities.

Effect of CuZnAl particles addition on microstructure of Cu/Sn58Bi/Cu TLP bonding solder joints

In order to reduce the formation of voids in the Cu/Sn58Bi/Cu solder joints during transient liquid phase (TLP) bonding, the effect of CuZnAl particles on microstructure of Cu/SnBi/Cu TLP bonding solder joints was investigated. After bonding, the prism-type Cu6Sn5 intermetallic compounds (IMCs) were formed at the interface. The growth of Cu6Sn5 IMC grains was controlled by the interface reaction flux J2. The prism-type Cu3Sn IMCs grew at the expense of Cu6Sn5 IMCs. With the increase of bonding time, the solder joints were converted into all IMCs, indicating that SnBi solder and SnBi-0.5 CuZnAl solder are suitable for low-temperature bonding and high-temperature applications. When the CuZnAl particles were added, the growth of the interfacial IMCs was inhibited, and the formation of voids was significantly reduced.

Effect of flux doped with Cu6Sn5 nanoparticles on the interfacial reaction of lead-free solder joints

In this paper, flux doped with 0.05, 0.1, and 0.2 wt% Cu6Sn5 nanoparticles (NPs) were reasonably believed to affect the morphology and growth rate of the intermetallic compounds (IMC) between Cu substrate and Sn–3.0Ag–0.5Cu solder. Reflowing was performed at 250 °C, then isothermal aging was conducted at 150 °C up to 360 h. The experimental results show that the thickness of the IMC layer increased with the increment of aging time. When the aging time extended to 120 h or more, the Cu3Sn layer appeared on the side of the Cu substrate and also thickened as time increased. The additions of Cu6Sn5 NPs into the flux did not change the type of IMCs while the total thickness of the IMC changed visually. It was calculated that the corresponding growth rate constant of interfacial IMCs in solder joints with flux contained 0, 0.05, 0.1, and 0.2 wt% Cu6Sn5 NPs were 0.14766, 0.14719, 0.14578 and 0.14726 μm/h1/2, respectively. It means that adding Cu6Sn5 NPs into flux could effectively inhibit the growth of IMC layer. The strongest inhibition effect on the growth of IMC layer could be achieved when the content of Cu6Sn5 NPs was 0.1%. Flux with Cu6Sn5 NPs could also effectively inhibit the coarsening of the interfacial IMC grains, and adding 0.1% NPs to the flux has the best inhibition effect.

Effect of Bi on microstructure and mechanical properties of Sn-10Sb-1.5Cu (SSC1015) solder alloys

In this work, the new modified quaternary lead-free Sn-10Sb-1.5Cu-xBi ( x = 0, 0.5, 1, 5 wt%) solder alloys were prepared to research the effect of Bi addition on their thermal behaviors, microstructures and mechanical properties by employing differential scanning calorimetry (DSC), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), a tensile tester and a microhardness testing machine, respectively. The results showed that the melting temperature, pasty range and undercooling of Sn-10Sb-1.5Cu-based solders obviously decreased with addition of Bi ranging from 0 to 5 wt%. It was found that Sn3Sb2 and Cu6Sn5 intermetallic compounds (IMCs) were formed during casting and no other IMC contenting Bi element were observed within the solder matrix of Sn-10Sb-1.5Cu (SSC1015) solders with various Bi contents. With the increasing Bi element in SSC1015 solders, both the ultimate tensile strength (UTS) and microhardness of samples increased since the finer and thinner IMCs grains were produced, with UTS and microhardness being 72.91 MPa and 26.80 HV for SSC1015 while 113.66 MPa and 35.78 HV for SSC1015-5Bi, respectively. Moreover, the influences of thermal aging on SSC1015-xBi solders were also studied in this work. It was found that both Sn3Sb2 and Cu6Sn5 IMCs within the Sn-rich phase increased in size after aging at 170 °C for 72 h and thus led to deterioration of mechanical properties, including UTS and microhardness of samples.

Research on Interfacial Reaction and Growth Behavior of Intermetallic Compound of Dip-Soldered Sn/Ni System

Interfacial reaction and the growth behavior of intermetallic compound (IMC) between Sn solder and Ni substrate by dip soldering under different aging conditions (120 °C, 170 °C and 200 °C) by using scanning electron microscope were investigated. Experimental results showed that the only scallop-shaped Ni3Sn4 IMC layer formed at the interface after aging process and the thickness of IMC layer increased with prolonged aging time. Moreover, the cracks formed in the interface between IMC and solder could be resulted from the residual stress caused by the difference in thermal expansion coefficients. In addition, the spalling behavior of IMC from substrate was caused by cyclic shear stresses and strains induced and the morphological changes in IMC formation. During the aging process, it was found that the thickness of IMC always had a linear relationship with the square root of aging time under different aging temperatures (120 °C, 170 °C and 200 °C). The growth rate constants of IMC layers aged at 120 °C, 170 °C and 200 °C were obtained by using fitting method from the experimental data, which were 4.65 × 10−18 m2 s−1, 9.94 × 10−18 m2 s−1 and 1.76 × 10−16 m2 s−1, respectively. Based on these data, the activation energy of IMC layer was determined to be 63.23 kJ/mol. Likewise, the mean diameter of IMC grains increased with the increase in aging time. It is suggested that the mean diameter of IMC grains was always plotted against the aging time on a double logarithmic scale under different aging temperatures. The time rate constants of IMC grains aged at 120 °C, 170 °C and 200 °C were obtained by using same method, which were 0.10, 0.27 and 0.26, respectively.

Interfacial microstructure and bonding strength of copper/aluminum clad sheets produced by horizontal twin-roll casting and annealing

The copper/aluminum (Cu/Al) clad sheets were produced on a horizontal twin-roll caster and annealed. The effects of annealing temperature on the interface and peel strength of the Cu/Al clad sheets were investigated. The interfacial microstructures of the as-cast and annealed reinforced clad sheets were analyzed. With the increase of annealing temperature, the growth of total intermetallic compound (IMC) layer accelerated, and the peel strength slightly increased and then decreased rapidly. For the as-cast and annealing reinforced clad sheets, the thicknesses of interface layers were less; the interfaces were mainly composed of two or three IMC grain layers; there are the almost coherent interfaces of Al2Cu/Al4Cu9, Al2Cu/Al and Al4Cu9/Cu. These structural characteristics of the interfaces can improve the peel strength of the clad sheets.

Microstructure evolution and mechanical properties of Cu/Sn/Ag TLP-bonded joint during thermal aging

Low-temperature transient liquid phase (TLP) bonding is a promising joining technology for high-temperature electronic devices packaging. However, the effect of thermal aging on the joint microstructure and performance has been rarely studied so far. In this paper, the relationship between microstructural evolution and mechanical property was developed for the Cu/Sn/Ag TLP-bonded joint during 350 °C aging. Experimental results show that an interfacial reaction occurs between the intermetallic compounds (IMCs) of Cu3Sn and Ag3Sn, which induces that a great amount of Cu3Sn particles or wedges embed into the Ag-Sn phase layer. The reaction process is controlled by a volume diffusion of Cu elements from the Cu substrate, and capable of promoting the transformation from Ag3Sn into Ag(Sn) solid solution. Cu41Sn11 phase can be formed at the expense of Cu3Sn and Cu, of which transformation process is completely achieved after aging for 480 h, and the Cu(Sn) solid solution intimately contacts with the opposite Ag(Sn) solid solution in many areas after aging for 960 h. The joint mechanical property initially declines due to the formation of Cu41Sn11 phase and Cu-Sn IMCs grain coarsening, and then increases because of the complete depletion of Cu3Sn and substantial precipitation of Cu(Sn) solid solution. After aging for nearly 1000 h, the joint still maintains a high shear strength of >40 MPa, indicating an excellent thermal reliability.

Effects of Sn addition on the microstructure and properties of Bi–11Ag high-temperature solder

High-temperature lead-free Bi–11Ag solder with a Sn addition of 1, 3, and 5 wt% was investigated in this paper. The results show that the melting temperature of Bi–11Ag solders dropped from 265 to 255 °C after the addition of Sn, which is suitable for the high-temperature reflow process. When the addition of Sn was 3 wt% or less, dendrites in the microstructure would be refined, however, further additions of Sn show an opposite effect. The contact angle of Bi–11Ag–xSn (x = 0, 1, 3, 5 wt%) solders on the Cu substrate was measured, and the value decreased from 62° to 41° with the increasing of Sn content. The tensile strength of the Cu/Bi–11Ag–xSn solder/Cu sandwich structured microscale solder joint continues to increase from 43.3 to 53.9 MPa and the fracture position evolves from the solder/Cu interface to the middle of solder. In addition, according to EDS analysis of the solder/Cu interface, a Cu3Sn intermetallic compound (IMC) layer can be identified. The combination of this IMC layer and grain boundary grooving at the solder/Cu interface can effectively improve the strength of the Bi–11Ag–xSn solder joint.

A Comparative Study on the Microstructure and Mechanical Properties of Cu6Sn5 and Cu3Sn Joints Formed by TLP Soldering With/Without the Assistance of Ultrasonic Waves

In this study, the microstructure and mechanical properties of Cu6Sn5 and Cu3Sn intermetallic joints, formed by the transient liquid phase (TLP) soldering process with and without the assistance of ultrasonic waves (USWs), were compared. After the application of USWs in the TLP soldering process, Cu-Sn intermetallic compounds (IMCs) exhibited a novel noninterfacial growth pattern in the molten solder interlayer. The resulting Cu6Sn5 and Cu3Sn joints consisted of refined equiaxed IMC grains with average sizes of 3 and 2.3 µm, respectively. The Cu6Sn5 grains in the ultrasonically soldered intermetallic joints demonstrated uniform mechanical properties with elastic modulus and hardness values of 123.0 and 5.98 GPa, respectively, while those of Cu3Sn grains were 133.9 and 5.08 GPa, respectively. The shear strengths of ultrasonically soldered Cu6Sn5 and Cu3Sn joints were measured to be 60 and 65 MPa, respectively, higher than that for reflow-soldered intermetallic joints. Ultrasonically soldered Cu6Sn5 and Cu3Sn joints both exhibited a combination of transgranular and intergranular fractures during shear testing.

Effect of Ni addition to the Cu substrate on the interfacial reaction and IMC growth with Sn3.0Ag0.5Cu solder

The formation and growth of intermetallic compound (IMC) layer at the interface between Sn3.0Ag0.5Cu (SAC305) solder and Cu–xNi (x = 0, 0.5, 1.5, 5, 10 wt%) substrate during reflowing and aging were investigated. The soldering was conducted at 270 °C using reflowing method, following by aging treatment at 150 °C for up to 360 h. The experimental results indicated that the total thickness of IMC increased with increasing aging time. The scallop-like Cu6Sn5 and planar-like Cu3Sn IMC layer were observed between SAC305 solder and purely Cu substrate. As the content of Ni element in Cu substrate was 0.5% or 1.5%, the scallop-like Cu6Sn5 and planar-like Cu3Sn IMC layer were still found between solder and Cu–Ni substrate and the total thickness of IMC layer decreased with the increasing Ni content. Besides, when the Ni content was up to 5%, the long prismatic (Cu,Ni)6Sn5 phase was the only product between solder and substrate and the total thickness of IMC layer increased significantly. Interestingly, the total thickness of IMC decreased slightly as the Ni addition was up to 10%. In the end, the grains of interfacial IMC layer became coarser with aging time increasing while the addition of Ni in Cu substrate could refine IMC grains.

Comparative study on the isothermal aging of bare Cu and ENImAg surface finish for Sn-Ag-Cu solder joints

The surface finish of electroless nickel/immersion silver (ENImAg) has been developed as an alternative to lead-free surface finish in electronic industry for the reduction of metal cost without affecting the reliability and solderability performance. In this study, different types of lead-free solders, Sn-3.0Ag-0.5Cu (SAC305) and Sn-4.0Ag-0.5Cu (SAC405) were involved along with ENImAg and bare copper substrate in order to investigate the formation of intermetallic compounds (IMCs) under reflow and aging time. The characterization and analysis of the samples conducted through scanning electron microscopy and energy dispersive x-ray. As a result, the IMCs of SAC/Cu which were formed on the interface were Cu6Sn5 and Cu3Sn. Unlike the reaction displayed by SAC/Cu, the IMCs of SAC/ENImAg which were formed on the interfaces, were identified as (Cu,Ni)6Sn5) and (Ni,Cu)3Sn4. The kinetic growth of each IMC was analyzed. It was found that IMC of SAC/Cu was thicker than IMC of SAC/ENImAg. Upon the revelation of these observations, ENImAg surface finish reduced the growth of IMC and smaller grains size compared to bare Cu.

Joule heating dominated fracture behavior change in micro-scale Cu/Sn-3.0Ag-0.5Cu/Cu(Ni) joints under electro-thermal coupled loads

Joule heating dominated fracture position transition from the interface between the solder and the intermetallic compound (IMC) layer to the solder matrix occurs in micro-scale Cu/Sn-3.0Ag-0.5Cu/Cu(Ni) joints under electro-thermal coupled loads with a high current density and increasing temperature. The interfacial fracture is triggered by localized-melting of the solder induced by current crowding at grooves of the interfacial IMC grains and driven by the strain mismatch between the solder and the interfacial IMC layer, while fracture in the solder matrix is caused by matrix bulk melting and the constraint effect from the interfacial IMC layer-substrates.

In situ Synthesis of Al-Cr/Al Composites and Bending Property

Al-Cr/Al composites were fabricated by ultrasonic vibration assisted. Then the reinforced phase were characterized by XRD and EDS, the reinforcement particle size, morphology and distribution were observed by the use of SEM, and studied on the bending property of the composite material. The result shows that, Al and Cr generate inter-metallic compounds of Al0.983Cr0.017, Al5Cr, -Al8Cr5, -AlCr2, etc. The enhance particles, appear irregular polygonal shape, smaller particles diameter, distribute in the matrix uniformly. And the enhance particles and the matrix get good bond, clean interface, non-pollution. The bending strength bb of the composites is decline as increasing Cr content. It is easy to form stress concentration at the interface. Inter-metallic compounds grain are not easy to slip under external load force, reinforcing particles and the matrix are easy to suddenly fall off, so, composites have a greater brittle.

Effect of intermetallic compounds on mechanical properties of copper joints ultrasonic-soldered with Sn-Zn alloy

The transformation of the intermetallic compounds (IMC) at the interface of Sn-Zn solder and Cu substrate by an ultrasonic-assisted soldering method with the variation of Zn content was investigated. The formation of IMC at the solder/Cu interface is controlled by the Zn content in the filler metals. The IMC layer of Cu6Sn5 forms if the mass fraction of Zn is lower than 0.5wt.%. The IMC becomes a single-layered Cu5Zn8 if the mass fraction of Zn exceeds 1wt.%. The layer of Cu5Zn8 thickens with the increase of Zn content. Joints with an IMC layer of Cu5Zn8 exhibit a higher strength than that with Cu6Sn5. In the joints soldered with the Sn-0.5Zn filler metal, fractures occur inside the Cu6Sn5 IMC grains. In the joints with the Zn content higher than 1wt.%, fractures propagate along the Cu5Zn8 IMC/solder interface. The locations of the fracturing are associated with the micro-cracks that existed at the IMC grains.